U.S. Pat. No. 5,402,327 entitled "Simplified Safety Syringe with Retractable Self-biased Needle" issued to the same inventor of this application diclosed a safety syringe including:a hollow needle normally held in a front portion of a syringe, a coupling member of arrowhead shape integrally formed with the thin-disk plunger, an annular ring embedded on the plunger to allow the plunger to be slibably held in the syringe for injection use, the coupling member formed on the plunger engageable with a biasing socket recessed in a rear needle portion of the hollow needle and with the biasing socket generally formed as a conical shape having a longitudinal conical axis inclined from a needle axis of the needle, wherby upon retraction of the plunger and the coupled needle into the syringe, the needle will be inclined to prevent a further outward protoruding of the retracted needle.
However, the needle portion 21 having an arcunte packing ving 26a circumferentialy disposed around the shank portion 22 to be engageably held in the ving groove 120a in the sleeve portion 12, Since the safety syringe is always made as disposable and will be disposed once being used for hygienic reason, such a big plunger, which is always made of resilient rubber materials, will waste money and will also increase a burden for waste disposal and treatment on a viewpoint of environmental protection.